The present invention relates generally to invasive devices and methods for treatment of the heart, and specifically to devices and methods for controlling the heart muscle during surgery.
Heart surgery is often accompanied by the induction of cardioplegia (elective stopping of essentially all cardiac activity by injection of chemicals, selective hypothermia, mechanical stabilization, or electrical stimuli). In humans, induced global cardioplegia is nearly always practiced in conjunction with cardiopulmonary bypass.
Recently, minimally-invasive methods of cardiac surgery have been developed, in which the heart is approached through an incision made between the ribs, without sternotomy. It is sometimes preferred that, rather than inducing cardioplegia, the surgeon mechanically restrains a portion of the heart on which a surgical procedure, such as a bypass graft, is to be performed. Various tools and methods have been developed for this purpose, such as: (a) a suction cup-based stabilization platform (e.g., the Utrecht Octopus); (b) mechanical stabilization devices, such as the Ultima OPCAB System, produced by Guidant, Inc. (Indianapolis, Ind.); (c) the Octopus 2 or the EndoOctopus device, both produced by Medtronic, Inc. (Minneapolis, Minn.); (d) a U-shaped metal foot and other stabilizers produced by Genzyme Surgical Products, Inc. (Tucker, Ga.); (e) the Octopus Suction stabilizer, produced by Medtronic GmbH, Germany; and (f) CardioVations mechanical stabilizers produced by Ethicon Endo-Surgery (Cincinnati, Ohio).
An article entitled xe2x80x9cCoronary artery bypass grafting without cardiopulmonary bypass and without interruption of native coronary flow using a novel anastomosis site restraining device (xe2x80x98Octopusxe2x80x99),xe2x80x9d by Borst et al., Journal of the American College of Cardiology, 27(6) (May 1996), pp. 1356-1364, which is incorporated herein by reference, describes use of the Octopus suction-generating device during experimental surgery on in situ pig hearts.
Such mechanical restraint of the heart muscle requires that substantial force, e.g., pressure or vacuum, be applied, which can cause tissue trauma. The effects of mechanical stabilization are described in an article, xe2x80x9cThe effects of mechanical stabilization on left ventricular performance,xe2x80x9d by Burfeind et al., European Journal of Cardio-Thoracic Surgery, 14(1998), pp. 285-289, which is incorporated herein by reference.
It is an object of some aspects of the present invention to provide improved methods and apparatus for regulating motion of the heart.
It is a further object of some aspects of the present invention to provide improved methods and apparatus for reducing motion of the heart during minimally-invasive and open-chest surgery.
It is yet a further object of some aspects of the present invention to provide improved methods and apparatus for applying mechanical force to reduce motion of the heart during minimally-invasive and open-chest surgery.
It is still a further object of some aspects of the present invention to provide improved methods and apparatus for reducing motion of the heart during minimally-invasive and open-chest surgery, while minimizing or substantially eliminating injury to the heart resulting from the motion reduction.
In preferred embodiments of the present invention, cardiac control apparatus inhibits motion of a segment of a patient""s heart, while allowing the heart to continue to pump blood. The reduction in motion of the segment, as provided by these embodiments of the present invention, is typically used to enable a surgeon to perform minimally-invasive surgery or open-chest surgery, generally without inducing global cardioplegia or requiring cardiopulmonary bypass. The cardiac control apparatus comprises a stabilization element, which has a surface that is applied to the heart in order to reduce motion thereof. Additionally, a plurality of suction ports are positioned on the surface of the stabilization element. When the element is applied to the segment of the heart, the ports apply suction to the segment of the heart, so as to maintain contact between the heart and the stabilization element, and to thereby reduce motion of the segment. Preferably, the ports are configured such that if one of the suction ports loses contact with the surface of the heart, at least one of the other ports will continue to apply suction to the heart. In this manner, the loss of contact substantially does not inhibit the overall functioning of the cardiac control apparatus.
By contrast to these embodiments of the present invention, prior art mechanical stabilizers (such as the Medtronic Octopus) fix a plurality of suction ports to the stabilization element in a configuration that assures that if even one of the suction ports loses contact with the heart, then all of the suction ports will fail to operate. In order to avoid this eventuality, prior art mechanical stabilizers must apply a high level of suction through each of the ports (e.g., 400 millibars), so as to guarantee that throughout the medical procedure, all of the suction ports maintain their contact with the heart. The inventors believe that the application of such a strong suction to the epicardium risks injuring the affected tissue. This structural drawback of prior art stabilizers derives from their use of a single suction line that is directly coupled to all of the ports. Thus, if one of the ports even temporarily loses contact with the heart, then it effectively causes a short-circuit, whereby that port becomes the path of least resistance for air to flow into the suction line, and the desired negative air pressure at the other suction ports disappears.
Therefore, an advantage of these embodiments of the present invention is that significantly lower levels of suction can be applied through every port, because at least some of the suction ports will continue to function even if some others of the suction ports have lost contact with the surface of the heart. It is believed that these lower levels of suction (typically under 200 millibars) will substantially reduce or eliminate injury to the heart responsive to the application of suction thereto.
In a preferred embodiment of the present invention, each of the suction ports is coupled by a respective suction line to a vacuum source, typically external to the stabilization element. In this configuration, each suction port acts substantially independently of each of the other ports, and is therefore unaffected by whether the other ports are in contact with the heart.
Alternatively, at least one of the suction lines has a plurality of suction ports coupled thereto. This configuration allows greater simplicity of the stabilization element, by reducing the number of suction lines used to hold the surface of the heart in contact with the stabilization element. Preferably, a sufficient number of suction lines are utilized such that even if one of the ports on a multi-port suction line failsxe2x80x94thereby generally disabling the other ports on the same linexe2x80x94one or more other ports not coupled to the same line will still continue to function. Optionally, some or all of the ports coupled to the multi-port suction line are coupled thereto through respective valves, which are adapted to close when the suction port loses its seal with the surface of the heart. In this manner, even when a plurality of ports are coupled to the same line, the failure of one of the ports does not adversely affect the functioning of the other ports.
For some applications of the present invention, a plurality of ports on the surface of the stabilization element are coupled through respective small orifices to a relatively-large chamber, typically within the stabilization element. The chamber is coupled, in turn, to the vacuum source. Preferably, the volume of the chamber is sufficiently large and the cross-sectional areas of the orifices are sufficiently small, such that if one of the suction ports loses its seal with the heart, and air enters the chamber through the orifice coupled to the port, then the negative pressure within the chamber will not be significantly affected. Since the overall negative pressure within the chamber substantially does not change when one of the ports coupled thereto loses its seal with the heart, the other ports coupled to the chamber will continue to function.
In a preferred embodiment, a control unit of the cardiac control apparatus or a human operator of the apparatus reduces the level of suction applied by some or all of the ports, until at least one of the ports loses its seal with the surface of the heart. At this point, most or all of the other ports preferably continue to apply suction, because the stabilization element is preferably configured such that some of the ports can continue to apply suction even when some others of the ports lose effective contact with the heart. It is noted that this embodiment of the present invention allows the cardiac control apparatus to operate at suction levels significantly lower than are possible using the prior art apparatus described hereinabove, because the prior art apparatus must apply high levels of suction so as to guarantee that all of the suction ports are operative.
In a preferred embodiment, the level of suction applied by one or more of the ports is intermittently or continuously varied, responsive to measurements indicative of the number of suction ports which are effectively securing the heart. Optionally, the suction level is also set based on measurements indicative of a physiological parameter, such as heart rate, left ventricular pressure (LVP), or motion of the heart. For example, suction may be decreased responsive to a decrease in the patient""s heart rate, because reduced heart rate is typically associated with a lower probability that the suction ports will lose effective contact.
In a preferred embodiment, the level of applied suction is modulated in coordination with other means for stabilizing the segment of the heart, e.g., cardioplegia-inducing drugs, mechanical force applied by the stabilization element, or electrical signals applied to the heart. For example, if the application of cardioplegia-inducing drugs is being decreased, the level of suction may be increased.
Optionally, electrical signals are applied through electrodes fixed to the stabilization element or placed directly on the surface of the heart. Preferred methods and apparatus for applying signals to the heart, as well as for detecting electrical activity generated by the heart, are described in a PCT patent application entitled, xe2x80x9cLocal cardiac motion control using applied electrical signals and mechanical force,xe2x80x9d filed May 25, 2000, and in U.S. patent application Ser. No. 09/320,090, entitled xe2x80x9cLocal cardiac motion control using applied electrical signals.xe2x80x9d Both of these applications are assigned to the assignee of the present patent application and are incorporated herein by reference. In addition, signals described in PCT Patent Publication WO 97/25098, and in the corresponding U.S. National Phase patent application Ser. No. 09/101,723, entitled, xe2x80x9cElectrical muscle controller,xe2x80x9d may be applied to the heart through electrodes coupled to the stabilization element or through electrodes applied directly to the heart. Typically, the level of suction is increased or decreased in coordination with the signals applied to the heart, so as to reduce motion of the segment while generally assuring that systemic oxygen demands are met.
There is therefore provided, in accordance with a preferred embodiment of the present invention, apparatus for performing a medical procedure on a beating heart, including:
a stabilization element, adapted to be applied to a segment of the heart in order to reduce motion of the segment;
a plurality of suction ports, positioned on the stabilization element so as to form respective seals with the segment of the heart while the stabilization element is applied to the segment, which suction ports are adapted to apply suction forces to the segment of the heart so as to maintain the segment in contact with the stabilization element; and
a suction control assembly, coupled to the ports, such that at least one of the suction ports is adapted to maintain its seal with the segment of the heart even when another one of the suction ports does not form a seal with the segment of the heart.
Preferably, the suction control assembly includes:
a first suction line, adapted to convey negative air pressure to a first one of the suction ports; and
a second suction line, adapted to convey negative air pressure to a second one of the suction ports,
wherein a level of negative air pressure in the first suction line is substantially independent of a level of negative air pressure in the second suction line, when the stabilization element is applied to the segment of the heart.
Alternatively or additionally, the suction control assembly includes:
a first suction line, which is adapted to convey negative air pressure to two or more of the suction ports; and
a second suction line, which is adapted to convey negative air pressure to one or more of the suction ports,
wherein a level of negative air pressure in the second suction line is substantially independent of a level of negative air pressure in the first suction line, when the stabilization element is applied to the segment of the heart.
Further alternatively or additionally, the suction control assembly includes a valve coupled to one of the suction ports, which valve is adapted to close when the suction port coupled thereto does not form a seal with the segment of the heart.
In a preferred embodiment, the stabilization element is adapted to be applied to the segment of the heart so as to enable a therapeutic medical procedure to be performed on the heart. Alternatively or additionally, the stabilization element is adapted to be applied to the segment of the heart so as to enable a diagnostic medical procedure to be performed on the heart.
In a preferred embodiment, the suction control assembly includes a chamber having negative air pressure therein when the stabilization element is applied to the segment of the heart. The chamber is coupled through respective orifices to the suction ports. A characteristic of the orifices is such that, when one of the suction ports does not form a seal with the segment of the heart, a magnitude of the negative air pressure within the chamber is maintained to such an extent that one or more of the other suction ports maintain their seals with the segment of the heart. Preferably, the characteristic of the orifices includes cross-sectional areas of the orifices.
Alternatively or additionally, the apparatus includes:
a vacuum source, adapted to generate negative air pressure; and
a control unit, adapted to couple the negative air pressure to the plurality of suction ports, so as to apply to the segment of the heart the suction forces which maintain the segment in contact with the stabilization element.
In a preferred embodiment, the control unit is adapted to couple the negative air pressure to the suction ports, such that a first one of the suction ports applies to the segment of the heart a first level of negative air pressure, and a second one of the suction ports applies to the segment of the heart a second level of negative air pressure.
In a preferred embodiment, the apparatus includes a force sensor, adapted to convey to the control unit a force signal responsive to a force applied by the stabilization element to the segment of the heart, wherein the control unit is adapted to modulate a magnitude of the negative air pressure applied to one or more of the suction ports responsive to the force signal.
Alternatively or additionally, the apparatus includes a sensor, adapted to convey to the control unit a sensor signal indicative of a number of the suction ports not forming a seal with the segment of the heart, wherein the control unit is adapted to modulate a magnitude of the negative air pressure applied to two or more of the ports, so as to generally maintain a determined number of the suction ports not forming respective seals with the segment of the heart. In a preferred embodiment, the control unit is adapted to modulate the magnitude of the negative air pressure applied to two or more of the ports, so as to generally maintain exactly one of the suction ports not forming a seal with the segment of the heart.
Optionally, the apparatus includes an electrode, adapted to be placed on the heart and to convey a signal to the control unit responsive to electrical activity of the heart, wherein the control unit is adapted to modulate a magnitude of the negative air pressure applied to one or more of the suction ports responsive to the signal. Further optionally, the electrode is fixed to the stabilization element.
In a preferred embodiment, the apparatus includes a motion sensor, adapted to convey to the control unit a motion signal responsive to motion of the heart, wherein the control unit is adapted to modulate a magnitude of the negative air pressure applied to one or more of the suction ports responsive to the motion signal. Optionally, the motion sensor is fixed to the stabilization element. Further optionally, the control unit is adapted to reduce the magnitude of the negative air pressure responsive to a motion signal indicative of reduced motion of the heart. Alternatively or additionally, the control unit is adapted to increase the magnitude of the negative air pressure responsive to a motion signal indicative of increased motion of the heart.
In a preferred embodiment, the apparatus includes a sensor, coupled to the control unit and to the suction ports, wherein the control unit is adapted to reduce a magnitude of the negative air pressure applied to two or more of the ports, and to terminate reducing the magnitude of the negative air pressure when the sensor conveys a sensor signal indicative of one or more of the suction ports not forming respective seals with the segment of the heart. Typically, the sensor includes an air-pressure sensor or an air-flow sensor.
In a preferred embodiment, the apparatus includes an electrode, adapted to be placed on the heart, wherein the control unit is adapted to drive the electrode to apply a signal to the heart which modulates mechanical behavior of the heart. Preferably, the electrode is fixed to the stabilization element. Further preferably, the control unit is adapted to drive the electrode to apply the signal to the heart so as to reduce motion of the heart. Optionally, the control unit is adapted to regulate a magnitude of the negative air pressure applied to the segment of the heart by at least one of the suction ports in conjunction with driving the electrode to apply the signal.
In a preferred embodiment, the plurality of suction ports include:
a test port; and
a set of other ports,
wherein, for a given level of negative air pressure applied to the test port and to the set of other ports, the other ports are adapted to have a higher probability than the test port of remaining sealed to the segment of the heart.
Preferably, the test port includes a pressure regulator including an input and an output thereof, the pressure regulator being adapted to be coupled at the input to air at a first magnitude of air pressure, and to be coupled to apply, at the output, air at a second magnitude of air pressure which is lower than the first magnitude.
There is further provided, in accordance with a preferred embodiment of the present invention, a method for performing a medical procedure on a beating heart, including:
applying a stabilization element to a segment of the heart, so as to reduce motion of the segment; and
applying suction forces to the segment of the heart through a plurality of suction ports that are positioned on the stabilization element, so as to form respective seals with the segment of the heart while the stabilization element is applied to the segment, and so as to maintain the segment in contact with the stabilization element,
such that at least one of the suction ports maintains its seal with the segment of the heart even when another one of the suction ports does not form a seal with the segment of the heart.
In a preferred embodiment, applying the suction forces includes conveying negative air pressure to first and second ones of the suction ports, such that a level of the negative air pressure conveyed to the first suction port is substantially independent of a level of the negative air pressure applied to the second suction port, when the stabilization element is applied to the segment of the heart.
Alternatively or additionally, applying the suction forces to the segment of the heart includes:
conveying negative air pressure to two or more of the suction ports through a first suction line; and
conveying negative air pressure to one or more of the suction ports through a second suction line,
wherein a level of negative air pressure in the second suction line is substantially independent of a level of negative air pressure in the first suction line, when the stabilization element is applied to the segment of the heart.
In a preferred embodiment, applying the suction forces includes conveying negative air pressure from a chamber through respective orifices to the suction ports, such that, when one of the suction ports does not form a seal with the segment of the heart, a magnitude of the negative air pressure within the chamber is maintained to such an extent that one or more of the suction ports maintain their seals with the segment of the heart.
Alternatively or additionally, applying the suction forces includes closing a valve coupled to one of the suction ports when the suction port coupled to the valve does not form a seal with the segment of the heart.
In a preferred embodiment, applying the suction forces includes regulating negative air pressure applied to the suction ports such that a first one of the suction ports applies to the segment of the heart a first magnitude of negative air pressure, and a second one of the suction ports applies to the segment of the heart a second magnitude of negative air pressure.
Preferably, regulating includes:
regulating the second magnitude of negative air pressure to be lower than the first magnitude, while generally simultaneously reducing the first and second magnitudes of negative air pressure; and
discontinuing reducing the magnitudes of negative air pressure when the first port forms a seal and the second port does not form a seal.
In a preferred embodiment, the method includes receiving a force signal responsive to a force applied by the stabilization element to the segment of the heart, wherein applying the suction forces includes modulating a magnitude of negative air pressure applied to one or more of the suction ports responsive to the force signal.
Alternatively or additionally, the method includes receiving a signal responsive to electrical activity of the heart, wherein applying the suction forces includes modulating a magnitude of the negative air pressure applied to one or more of the suction ports responsive to the signal.
Further alternatively or additionally, the method includes receiving a motion signal responsive to motion of the heart, wherein applying the suction forces includes modulating a magnitude of the negative air pressure applied to one or more of the suction ports responsive to the motion signal. Preferably, modulating the magnitude of the negative air pressure includes reducing the magnitude of the negative air pressure responsive to a motion signal indicative of reduced motion of the heart. Alternatively or additionally, modulating the magnitude of the negative air pressure includes increasing the magnitude of the negative air pressure responsive to a motion signal indicative of increased motion of the heart.
In a preferred embodiment, applying the suction forces includes:
reducing a magnitude of the negative air pressure applied to two or more of the ports;
receiving a signal which is indicative of one or more of the suction ports losing their respective seals with the segment of the heart responsive to the reduced magnitude of the negative air pressure; and
terminating reducing the magnitude of the negative air pressure responsive to receiving the signal.
In a preferred embodiment, the method includes driving an electrode to apply a signal to the heart which further reduces motion of the heart. Preferably, applying the suction forces includes regulating a magnitude of the suction forces applied by one or more of the suction ports to the segment of the heart in conjunction with driving the electrode to apply the signal.
In a preferred embodiment, the method includes receiving a sensor signal indicative of a number of the suction ports not forming a seal with the segment of the heart, wherein applying the suction forces includes modulating a magnitude of the negative air pressure applied to two or more of the ports, so as to generally maintain a determined number of the suction ports not forming respective seals with the segment of the heart. Preferably, modulating the magnitude of the negative air pressure includes modulating the pressure so as to generally maintain exactly one of the suction ports not forming a seal with the segment of the heart.